An oxidation catalysis device, also referred to as a DOC device or DOC, standing for “diesel oxidation catalyst”, is a device placed in the exhaust line of a diesel-engined vehicle, as far as possible as close as possible to the engine so that it reaches its operating temperature of between 150° C. and 200° C. as quickly as possible, and which uses the oxygen of several of the components of the exhaust gas to perform oxidation, notably via the following three oxidation reactions:
oxidation of carbon monoxide (CO),
oxidation of hydrocarbons (HC),
oxidation of an organic fraction of the diesel particulates (SOF).
An oxidation catalysis device in an exhaust line generally assumes at least three main functionalities, which are:                1. converting CO and HC into carbon dioxide (CO2) and water (H2O),        2. creating an exothermal reaction for a determined length of time so as to regenerate a particulate filter positioned downstream of the DOC device in an exhaust line, where appropriate, and        3. oxidizing as much nitrogen monoxide (NO) as possible to convert it into nitrogen dioxide (NO2) in order to make a device of SCR (selective catalytic reduction) type positioned downstream in the exhaust line, where appropriate, more effective.        
Legislative requirements in a great many countries demand the monitoring of the functionalities of a DOC device while it is in use, particularly the functionality of converting carbon monoxide (CO) and/or hydrocarbons into carbon dioxide (CO2) and water (H2O).
Document EP2216522A1 discloses a method for monitoring an oxidation catalytic converter placed in an exhaust line of an internal combustion engine, in which method a diagnosis of the catalytic converter involves a test cycle during which the ability of the oxidation catalytic converter to convert hydrocarbons (HC) is determined on the basis of a temporary exothermal reaction generated by the post-injection of a given quantity of fuel into the catalytic converter. The exothermal reaction obtained is then compared against an expected correct exothermal reaction model, in order to establish a diagnosis of the oxidation catalytic converter as part of the OBD (which stands for on-board diagnostics).
Such a method has the chief disadvantage that its efficiency is dependent on the accuracy of the model and on the spread of the parameters used in the model, notably the quantity of fuel injected, the flow rate of the gases, the catalyst, leading to a spread in the temperature estimates themselves.